SAN DIEGO COUNTY  The region’s worst freeway bottleneck in 2012 remained — for the fourth year in a row — the Barham Drive backup on state Route 78 in North County, according to a U-T San Diego analysis of traffic data.

But there’s hope for this 4.4-mile titan of tie-ups: New merging lanes are set to open in April on Route 78 through San Marcos. The change could end the bottleneck’s reign as the most severe in the county, though transportation officials declined to make specific predictions.

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The new lanes west of Interstate 15 are “going to help tremendously,” Gustavo Dallarda of the California Department of Transportation recently told San Marcos leaders.

Gone from the Top 10 list of worst bottlenecks is any mention of Interstate 15, historically one of the most clogged corridors in the county. The $1 billion I-15 express lanes project gets the credit for moving that freeway off the list.

Other familiar stretches of congestion continued — on interstates 5 and 805 and state routes 56 and 163, to the bane of coastal and central San Diego commuters. Two traffic crunches on state Route 52 made the list as well.

A newcomer to the Top 10 is a backcountry bottleneck at state Route 67 and Mussey Grade Road. That’s not because this area of gridlock in Ramona suddenly materialized. Instead, Caltrans installed traffic sensors on the highway last summer, giving the agency its first true measure of the rural tie-up.

This fifth annual U-T list was based on data from the Caltrans Performance Monitoring System, which uses various sensor tools to monitor traffic on more than 2,000 miles of roads in the county.

For purposes of its database, Caltrans defines a bottleneck as “a regularly occurring delay at a specific location due mostly to problems in the roadway design or cars entering the flow of traffic.”

Significant drops in speed between detectors embedded in the road — at least 20 mph and to a speed of less than 40 mph — trigger a bottleneck flag.

The worst bottlenecks are measured using their “total delay” in vehicle hours.

Barham at Route 78 led to a whopping 436,261 hours of delay in 2012, an increase of 23 percent from the previous year. That bottleneck far outpaced the runner-up: I-805 at Nobel Drive, which sucked away 318,443 hours.

Local transportation officials said there’s relief ahead for some of the region’s stubborn backups, including new lanes under construction on stretches of I-805 near Chula Vista and La Jolla.

Improvements are planned for other bottlenecks, but they’re still years away from completion. Those include I-5 in North County, where construction of new express lanes won’t start until 2015 at the earliest.

For big-picture perspective, consider that congestion on Los Angeles freeways is far worse than in San Diego County. For example, one bottleneck on Interstate 405 near Sunset Boulevard stretches for nearly 10 miles and costs drivers 647,419 hours of delay.